1. Field of the Invention
The present invention relates to displacement control valves incorporated in variable displacement compressors used in vehicle air conditioners. More particularly, the present invention pertains to a control valve having a mechanism for controlling the flow of refrigerant gas from a discharge chamber to a crank chamber and to a mechanism for controlling release of refrigerant gas from the crank chamber to a suction chamber.
2. Description of the Related Art
FIG. 12 is a diagram showing the flow of refrigerant gas in a prior art variable displacement compressor. The compressor includes a discharge chamber 121 and a crank chamber 122, which are connected to each other by a supply passage 123. The crank chamber 122 is connected to a suction chamber 124 by a bleeding passage 125. Refrigerant gas in an external refrigerant circuit 129 is drawn into the suction chamber 124 through a suction passage 128. A swash plate (not shown) is tiltably supported on a rotary shaft (not shown) in the crank chamber. Pistons are housed in cylinder bores and operably coupled to the swash plate. Each piston compresses refrigerant gas drawn into the corresponding cylinder bore from the suction chamber 124 and discharges the compressed gas to the circuit 130 via the discharge chamber 121.
An electromagnetic valve 126 is located in the crank chamber supply passage 123. The valve 126 selectively opens and closes the passage 123 for controlling the supply of refrigerant gas from the discharge chamber 121 to the crank chamber 122. A control valve 127 is located in the bleeding passage 125. The valve 127 adjusts the opening of the passage 125 in accordance with the pressure Pse in the suction passage 128 thereby controlling the amount of refrigerant gas released from the crank chamber 122 to the suction chamber 124. The pressure Pc in the crank chamber 122 is controlled by the valves 126 and 127. Adjustment of the pressure Pc in the crank chamber 122 changes the difference between the pressure Pc in the crank chamber 122 and the pressure in the cylinder bores thereby changing the inclination of the awash plate. Each piston reciprocates in the corresponding cylinder bore with a stroke in accordance with the inclination of the swash plate. The displacement of the compressor is varied accordingly.
In the above described prior art compressor, the electromagnetic valve 126 and the control valve 127 are constructed independently and located separately in different positions in the compressor. This complicates the mechanism for controlling the displacement of the compressor and increases the manufacturing cost of the compressor. Further, the compressor must have two large spaces for accommodating the two valves. This enlarges the compressor.